[meteorite-list] Spirit Mars Rover Could Emerge From Slumber Soon

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 19 Jul 2010 10:46:48 -0700 (PDT)
Message-ID: <201007191746.o6JHkmt4010681_at_zagami.jpl.nasa.gov>

http://www.spaceflightnow.com/news/n1007/19spirit/

Red Planet rover could emerge from slumber soon
BY STEPHEN CLARK
SPACEFLIGHT NOW
July 19, 2010

NASA officials say the best chance to hear from the napping Spirit rover
again will be in September or October, but the timing of the robot's
revival from winter hibernation is an engineering guessing game.

Spirit was forced to sleep by the cold winter in the Martian southern
hemisphere, where low sun angles were not sufficient to power the rover
through solar panels.

The stranded rover last communicated with Earth on March 22. Spirit has
been stuck in a sand pit known as Troy since April 2009, leaving the
rover tilted away from the sun and limiting its ability to produce
electricity.

The winter solstice at Spirit's location was May 13, and conditions
should now be improving. But the rover's batteries likely won't be
collecting enough sunlight to begin communicating again until September
or October.

Spirit's energy production had dipped to 134 watt hours before
controllers lost communications March 22.

"While we've passed winter solstice, and the sun is getting a little
higher in the sky, the intensity of the sun is still very low," said
Doug McCuistion, the director of NASA's Mars exploration program. "So we
actually don't think we're going to have enough power to hear from it
for another month-and-a-half or two months. The peak probability is
going to be in late September or early October."

But that's just a best guess, according to Steve Squyres, the top
scientist for the Spirit and Opportunity rovers from Cornell University.

"It depends on the power projections, which are obviously uncertain,"
Squyres said in an interivew last week. "It depends very much on how
much dust is on the solar arrays, and we have no way of monitoring that
at the current time. Our best guess is probably like October-ish, but
that's got a lot of uncertainty in it."

NASA's large communications antennas are regularly listening for
messages from Spirit, just in case the rover wakes up earlier than
predicted.

Then there's the concern that Martian dust has accumulated on Spirit's
solar arrays, the robot's lifeline to wake up from its winter slumber.

"The solar array panels were pretty dirty," McCuistion said. "If there
has not been a cleaning event, and through winter typically you don't
get those, the dust build-up on the arrays could be pretty significant.
So we don't know when we'll be getting enough power into the arrays to
actually get the batteries charged up and get the computers back online."

The dust reduces the efficiency of the craft's fixed solar arrays.
Occasional gusts of wind blow dust off the solar panels, giving the
rovers a jolt of electricity.

But the fortuitous wind gusts aren't common in winter, and if Spirit's
solar panels have collected more dust since March, the rover could face
a master clock fault.

"If you stack worst case on top of worst case, there is one failure mode
we could get into, in principle," Squyres said. "We think it's unlikely,
but it's possible. It's called a master clock fault. If we have a master
clock fault, we probably wouldn't hear from the vehicle until the next
time we had one of these cleaning events -- the gusts of wind that clean
the solar arrays."

Engineers believe Spirit is now in a low-power fault, in which the craft
only powers its master clock to periodically check its power status
until there is enough electricity to wake up and radio Earth or an
orbiting satellite, according to NASA.

"There are two different levels of faults," Squyres said. "One is
low-power fault mode, which we know the brand. We know that we've
tripped that, and we think if that's the fault mode that we're in, we
will come out of it sometime probably in October, with big error bars.
If the power has dipped lower than our projections say, which is
possible if there was some big dust event, the next level of fault
protection is the master clock fault. If that happens, it gets much
harder to predict when we might hear from it again."

McCuistion, NASA's top Mars official, said Spirit's sensitive
electronics are being exposed to temperatures they have never seen
before, even lower than worst-case testing conducted before the craft
launched.

"It's an environment Spirit's never encountered before," McCuistion
said. "Some of this is crossing your fingers and some of it is good
engineering guesses, but none of it is hard science because we just
haven't experienced this before."

If Spirit survives the winter, NASA is planning a series of geophysical
science experiments probing the Red Planet's interior, monitoring
weather and studying the composition of nearby soil.

Studying the deep interior of Mars has long been a high priority for
researchers, according to McCuistion.

Spirit will be used to track tiny wobbles in the rotation of Mars, which
could tell scientists whether the planet has a molten or solid core.

NASA gave up on removing Spirit from its sandy trap in January after 4.8
miles of driving across the bed of Gusev crater and into a range of
highlands called the Columbia Hills.

McCuistion said the value of Spirit's new science mission, buoyed by its
high ranking in researchers' decadal survey reviews, means the rover
isn't in danger of being shut down anytime soon.

"The cost is negligible, frankly," McCuistion said in an interview last
week. "It's not that expensive to do that kind of science."

Like most missions in NASA's portfolio, the rovers are the subject of an
annual review by independent scientists to gauge their research value.

"Getting an asset on the surface of Mars is so hard, that when you have
them there doing good science, it's a lot cheaper to keep them going,"
McCuistion said. "As long as they're doing good science, we're not going
to turn them off unless they turn themselves off."
Received on Mon 19 Jul 2010 01:46:48 PM PDT